JSSpecCompiler: Split Parser/SpecParser.cpp into 8 files

This SpecParser.cpp had an ever increasing number of lines and contained
an implementation of 8 different classes. So I figured out it's about
the time to split it.

No behavior change.

Meta/Lagom/Tools/CodeGenerators/JSSpecCompiler/Parser/AlgorithmStep.cpp

@@ -0,0 +1,60 @@
+/*
+ * Copyright (c) 2023-2024, Dan Klishch <danilklishch@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include "Parser/Lexer.h"
+#include "Parser/SpecParser.h"
+
+namespace JSSpecCompiler {
+
+Optional<AlgorithmStep> AlgorithmStep::create(SpecificationParsingContext& ctx, XML::Node const* element)
+{
+    VERIFY(element->as_element().name == tag_li);
+
+    auto [maybe_tokens, substeps] = tokenize_step(ctx, element);
+
+    AlgorithmStep result(ctx);
+    result.m_node = element;
+
+    if (substeps) {
+        // FIXME: Remove this once macOS Lagom CI updates to Clang >= 16.
+        auto substeps_copy = substeps;
+
+        auto step_list = ctx.with_new_step_list_nesting_level([&] {
+            return AlgorithmStepList::create(ctx, substeps_copy);
+        });
+        result.m_substeps = step_list.has_value() ? step_list->tree() : error_tree;
+    }
+
+    if (!maybe_tokens.has_value())
+        return {};
+    result.m_tokens = maybe_tokens.release_value();
+
+    if (!result.parse())
+        return {};
+    return result;
+}
+
+bool AlgorithmStep::parse()
+{
+    TextParser parser(m_ctx, m_tokens, m_node);
+
+    TextParseErrorOr<NullableTree> parse_result = TextParseError {};
+    if (m_substeps)
+        parse_result = parser.parse_step_with_substeps(RefPtr(m_substeps).release_nonnull());
+    else
+        parse_result = parser.parse_step_without_substeps();
+
+    if (parse_result.is_error()) {
+        auto [location, message] = parser.get_diagnostic();
+        m_ctx.diag().error(location, "{}", message);
+        return false;
+    } else {
+        m_expression = parse_result.release_value();
+        return true;
+    }
+}
+
+}